Various devices are known for monitoring traffic for the purpose of detecting violations of speed and anti-tailgating regulations. Examples of such systems are described in the following U.S. Patents: U.S. Pat. No. 3,840,848 describes a system for multiple vehicle gap detection and interval sensing. U.S. Pat. No. 3,690,233 describes apparatus for photographing passing cars. U.S. Pat. No. 4,173,010 describes a system for recording vehicle speed and photographing vehicles.
The existing systems for traffic monitoring have disadvantages: they often have difficulties distinguishing trucks from a chain of cars and they do not produce pictures in which the violating vehicle is consistently at the same distance from the camera, thus providing consistent positive identification of the vehicle.
Furthermore, existing systems do not provide comprehensive internal calibration and do not provide an output record of violations which includes confirmation of the calibration.